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Possible Solution for Old Edmund Scientific Clock Drive Clutch Issues

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#1 Vitez

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Posted 17 February 2021 - 04:38 PM

I believe that I have found a more specific answer to the clutch adjustment challenge on the old Edmund Scientific clock drive which have an unique and somewhat confusing clutch design. Here is my short story that may be of help:

 

I have updated my home built Cassegrain by adding a Crayford 10:1 focuser.

 

This led me to clean and restore my classic Edmund scientific 1"-shaft  pedestal mount that has a vintage ES Clock Drive used exclusively with this scope.

 

I could not get the clutch to grip properly and was very frustrated. I did find this archived link doing a Google search on this very subject https://www.cloudyni...lutch-question/ on CN but it only took me part of the way.

 

What made this a bit more frustrating is that I actually have the original one-page Information and Instructions sheet that came with the clock drive with the revision number 3/77. It does not describe how the clutch adjustment is made or what tools are required.

 

However, I have been able to figure this out with the assistance of a friend who is an armature astronomer, engineer and machinist.

 

I offer this possible solution to all in case anyone has encountered the same issue. Since the archived subject is still available and covers most of the design of the clutch assembly portion of the drive, I will only focus on the important omission.

 

What seems to be missing is that the clutch is adjusted via 2 empty non-threaded holes (a picture of these holes and a 3/4 view of the drive itself for identification are attached). I have seen this drive using either long thumb screws or set screws (with hex nuts for locking, mine uses the latter).

 

Once you have everything inserted correctly (leather washer, AL disc without threaded center hole, AL disc with threaded hole and 2 set screws and finally AL disc with 2 adjustment set screws and 2 open holes) and have added tension to the 2 screws on the outer disc "locking" the last 2 discs together as one "lock nut" on the RA shaft, you would then need to use the 2 open non-threaded holes to make the clutch tension adjustment (NOT THE 2 SCREWS!). This is both counterintuitive and leaves out the need for a tool of some kind to make the necessary adjustment. I have found that these holes should be used as a viewing port to see the set screws on the center disc. If these sew screws move out of view while adjusting you then need to tension the outer screws until there is no movement. 

 

Inserting 2 rods into these holes and spanning them with a large adjustable wrench would work or if you are handy you could make a simple tool yourself. If you have access to machining equipment this is very simple. I am surprised that this is neither mentioned in the original instructions nor is a tool mentioned at all. Actually, when reading the original instructions the adjustment procedure is covered by only one sentence and it is not clear.

 

Once you have a tool that can be inserted into the 2 open holes you can now add the final torque adjustment to fine tune the clutch.

 

The Tricky Part: Although, this is the key to the clutch adjustment, it requires some finesse. Turn your balanced scope on the RA by hand about 90 to 120 degrees clockwise and then counterclockwise from your center start point. If you feel that is is very loose you need to tighten the clutch using your new tool. If it loosens in one direction but tightens in the opposite direction your adjustment is too tight and you need to back the adjustment off a bit with your tool. There is an equilibrium point you need to find that allows a consistent tension on the clutch while turning your scope by hand (in either direction) yet applies enough tension to allow the clock drive to move your scope without slippage.

 

Testing: I tried testing the clutch adjustment by running the clock drive for 1 hour at a time and used blue tape on the shaft housing to identify movement. Once you have a coupe or more successful tests without the RA shaft tightening or loosening (in one direction) your set.

 

Since ES had no way of knowing what the size and weight of scope, counterweights and accessories would be used with these clock drives, I am amazed that they did not explain the clutch adjustment method more in-depth. One adjustment setting would not be applicable. 

 

Okay, this worked for me and I hope that it works for you. 

Attached Thumbnails

  • View Holes.jpg
  • ES Clock Drive Diagonal View.JPG

Edited by Vitez, 17 February 2021 - 07:22 PM.

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#2 Garyth64

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Posted 17 February 2021 - 09:06 PM

I didn't like the original clutch set up either.

I eliminated the need for the two screws altogether, and went with one threaded lever that would tighten every thing up.

 

The lever is loose until and object is found, then the lever it tightened to engage the CD.  And for another object, loosen the lever, move the scope, and retighten the lever.

 

Here's a picture of before:

 

clock drive view.jpg

 

and here's after:

 

Edmund 2.jpg

 

The large threaded washer that had the two holes was replaced with just a thick washer and the lever.

 

It worked very well for me this way, and I never had to fiddle with the end nut or the screws again.


Edited by Garyth64, 17 February 2021 - 09:13 PM.

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#3 Eric P

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Posted 18 February 2021 - 09:54 AM

Looks like you repainted the mount (or powder coated) and refinished the legs.  Can I see a pic of the whole setup?  I have a 4" F15 that I want to refinish and yours looks very well done!



#4 Garyth64

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Posted 18 February 2021 - 04:32 PM

The original paint on the mount was coming off so I sanded it some and just repainted it.  Actually, I sanded it a lot.

 

The wood legs I made out of a 1-3/8 plank of Oak.  I ripped the wood into 6pcs each 7/8".

 

tripod for Edmund.jpg

 

 


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#5 apfever

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Posted 18 February 2021 - 08:10 PM

It sure would be nice to see a picture of that one page in

 

 

What made this a bit more frustrating is that I actually have the original one-page Information and Instructions sheet that came with the clock drive with the revision number 3/77. It does not describe how the clutch adjustment is made or what tools are required.

 

It sure would be nice to see a picture of that Information and Instructions sheet. A picture of each side if double printed.

 

There were a variety of these drives, Two main versions, and both main versions could be used on the 5/8" shaft Junior mount or the 1" shaft or the 1.5" shaft mounts.  The 1.5" shaft mounts had a special shaft that was machined down to 1" on the end. The 5/8" motor assembly had a main hub piece with a smaller hole. 

 

Both of the pictured drives above were early versions with an outside collar bolted to the brass gear. Vitez's (Topic Starter) version is the 4 hole back plate, while Gary has the two hole back plate.  The 4 hole in particular  was the first version and not well designed. The two hole is simpler and works OK with the biggest drawback being NO Springs. The springless design is why it takes finesse to get the tension right.

I've restored a few, still have some complete unfinished ones, and I have both main versions. The 1st edition 4 hole back plate had detrimental practicality as I recall, so I never completely analyzed it. It may have had a complete engineering flaw but I don't remember for sure. 

 

The first thing I'd need to see is a picture of that single (1 or 2 pages) Information and Instructions sheet. I'd then pull out my motors and look into it all again with pictures.  Pictures.



#6 Vitez

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Posted 23 February 2021 - 04:11 PM

Per request, please see scanned image of the original Edmund Clock Drive Instructions.

 

A PDF was too large to upload in this forum but a screen capture seems to have worked and is still readable.

 

Please advise if you have found the information for which you were searching.Edmund Clock Drive.JPG



#7 apfever

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Posted 24 February 2021 - 04:08 AM

It looks like some one fiddled with your clutch. I've never seen the set screws with lock nuts. I've always seen thumb screws. The three plate system with 4 hole end plate never was good that I could figure. Adjustment should be with two thumb screws, not by turning the end plate with a spanner wrench. The special tool you refer to making is called a spanner wrench. 

 

The clutch system you have was quickly abandoned by Edmund in favor of the simpler 2 plates with two thumb screws. I never had to make the 3 plate system like yours work since I've always had the better version to replace with. The paper seems oriented to the newer style, and the paper isn't very well written. 

 

I think I still have one complete early 3 plate clutch, and some parts. I did have at least two early versions at some time. There were even differences in the two. I have no doubts that Edmund was floundering around and supplying a system that needed fiddling but people were making do with. Not terribly atypical in manufacturing a new product. I'll take a look at what I have left but doubt I'll find any obvious logical  intended operation.


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#8 PawPaw

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Posted 24 February 2021 - 08:16 AM

Vitez.......take a look at this thread,  specifically post #5.  You are missing the thumbscrews in what you call the "view holes" on your first post.  The allen screws with the nuts are simply there to hold the plexiglass pointer for the drive setting circle.

 

https://www.cloudyni...k#entry10735144

 

Cheers

 

Don



#9 Vitez

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Posted 24 February 2021 - 03:36 PM

Hi Don,

 

I appreciate your input.

 

You may be correct on the missing thumb screws but the "view holes" as I've referred to them are not threaded.

 

I do not see any way that thumb screws could be added unless you are telling me that the thumb screws thread into the second (middle) disc? This would then replace the current Allen Key set screws that are now in the middle disc?

 

I will say this, I purchased this clock drive over 30 years ago in the Edmund Scientific Surplus Room where I made many great finds. I recall buying it for only a few dollars (at most). It it quite possible that I ended up with a failed prototype unit or a customer's return.

 

All I can say is that the current method of adjusting the clutch works. I've never seen the plexiglass pointer and have never seen a diagram or pictures of the proper setup so this was a challenge to get working from the get-go. 

 

I would appreciate any additional information that you could offer and pictures would be greatly appreciated!

 

Thanks again,

Vitez


Edited by Vitez, 24 February 2021 - 03:37 PM.


#10 telescope200

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Posted 24 February 2021 - 11:24 PM

I think Don is right there. Was looking at the op drive and could see something was very odd about the arrangement. The third disk is a spacer for mounting the plexiglass pointer. The second disk is where you screw in the thumb screws. You tension the clutch by turning the thumb screws.... it's a pretty simple setup. You can see it's the setting circle version because it has the outside collar where the setting circle disk went, it slipped on and then you slid on a rubber o-ring to hold it in place.

 

I think I have this drive in storage, can always post pics.

 

Robert S


Edited by telescope200, 25 February 2021 - 10:55 AM.


#11 telescope200

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Posted 24 February 2021 - 11:40 PM

Diagram here btw, top of the page. Shows the two disk version.

 

http://photos1.blogg...1600/clock2.gif



#12 PawPaw

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Posted 25 February 2021 - 08:24 AM

I do not see any way that thumb screws could be added unless you are telling me that the thumb screws thread into the second (middle) disc? This would then replace the current Allen Key set screws that are now in the middle disc?

 

 

That is exactly what I am saying.  The last disk with the setscrews are not threaded on the outside holes.  The thumbscrews should thread completely through the second disk and also fit into the holes of the third disk that applies pressure to the clutch material (leather).  All the disks must line up to function properly.  also note the last disk threads onto the  hub shaft.  It can be tricky to find the sweet spot  where all three disks need to be.   Here are some more pics on the 3 disk version.  

 

Cheers

 

Don

 

 

Attached Thumbnails

  • 20201215_170710a.jpg
  • 20201215_155931a.jpg


#13 apfever

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Posted 25 February 2021 - 01:23 PM

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#14 apfever

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Posted 25 February 2021 - 01:24 PM

.

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#15 apfever

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Posted 25 February 2021 - 01:25 PM

.

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  • Ed clock drive.jpg


#16 apfever

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Posted 25 February 2021 - 01:31 PM

Two of the 3 plate assemblies in the red oval.  These are the top two plates in the assemblies. The bottom plate is the same across all varieties including the good 2 plate that works (used in upper right assemblies). 

I'll zero on the red oval and then to the restored assemblies in upper corner with an extra bottom piece. 

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  • P1010013.JPG


#17 apfever

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Posted 25 February 2021 - 01:57 PM

These are the top and middle plate of this variety Edmund drive. The 5 hole plate on the setting circle is steel, only steel plate of any type anywhere I've seen. The unit assembled on the bolt is a correct functional version. The pair on the setting circle were modified by some home shop head drilling out the threads from the 3 hole aluminum piece on the right. 

 

There is a decent logical functional system here with the common third bottom piece. The rusty set screws shown on the bolted assembly can be long enough to hold the optional pointer system for the setting circles. I've never bothered to think these through as I have no need for them. I've always used the simpler efficient two plate. Next is how it works to break it up.

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  • P1010015.JPG


#18 apfever

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Posted 25 February 2021 - 02:11 PM

This is the two plate system that Edmund went to and it works fine. This is identical to what is used on the threee plate units. The three plates just ad another top plate to this system. The loose disk is a bottom plate common to everything. It has a smooth slip center bore and two unthreaded dimples for the thumb screws to nest in. The dimples do not go all the way through so the leather gasket contact is a smooth full face plant. 

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  • P1010016.JPG

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#19 apfever

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Posted 25 February 2021 - 02:23 PM

Just to be clear here is the bottom of the bottom plate. I rotated the assembled restored units as well. This clutch assembly is pretty simple. The top plate is threaded on the center bolt and locked in place with the nyloc nut. The thumb screws thread through the two side holes and press on the bottom plate. The dimples in the bottom plate lock onto the thumb screw ends to keep from turning.   

 

For the 3 plate system you take off the nyloc nut and thread on the top 5 hole plate. The top plate is screwed down to contact the middle plate then rotated back off till the smooth holes align with the thumbscrew holes in the middle plate. Insert thumb screws. The top plate is them tightened against the middle plate using the set screws. This provides the lock nut action to keep the clutch from spinning on the center bolt. The bottom two plates are a normal clutch system with the thumb screws going through smooth open holes in the top plate. The top plate is a modified form of lock nut. The set screws in the top plate can be long enough to mount the optional pointer. 

 

There is a lot of stainless, some custom hidden, on these assemblies.

Attached Thumbnails

  • P1010017.JPG

Edited by apfever, 25 February 2021 - 03:27 PM.

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#20 apfever

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Posted 25 February 2021 - 02:32 PM

Here is a full function 3 plate. The rusty set screw would have to be extra long to accommodate a nut and the optional pointer. 

 

I found original emblem thumb screws and will put this with the Edmund 8" extra parts from which it came. The motor is Cramer as stated in the Edmund catalogs and dated Sept. 1974.

Attached Thumbnails

  • P1010020.JPG

Edited by apfever, 25 February 2021 - 03:20 PM.

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#21 Garyth64

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Posted 25 February 2021 - 03:27 PM

Of those 3 plates, which ones are threaded?

 

I'm just not seeing how the two thumb screws tighten anything .


Edited by Garyth64, 25 February 2021 - 03:28 PM.


#22 PawPaw

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Posted 25 February 2021 - 04:45 PM

Of those 3 plates, which ones are threaded?

 

I'm just not seeing how the two thumb screws tighten anything .

Two.....The one with the setscrews (Setting circle sets against it) and the middle one.



#23 apfever

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Posted 25 February 2021 - 07:21 PM

First the brass gear slips onto the bolt.

Second the leather gasket slips onto the bolt.

 

Third the clutch plate with the smooth center hole and two unthreaded dimples slips onto the bolt. 

      The above plate goes on with the solid smooth side towards the leather gasket.

 

Fourth the plate with the three threaded holes (big center hole and two smaller side holes) threads onto the bolt.

      The above plate is what the thumb screws will thread into. At this time the plate is threaded onto the center bolt till it just touches the first plate.   

 

Fifth the plate with the 5 holes (three threaded and two smooth) threads onto the bolt.  A this time the plate is threaded on till it just touches the previous middle plate. 

 

You will now have all three plates installed and all of them lightly nested together, and all lightly against the leather gasket.  

The last plate is now backed off (unscrewed) just enough to align it's smooth outer holes with the threaded thumb screw holes of the middle plate.

Install the thumb screws through the smooth holes of the last plate and thread them into the aligned holes of the middle plate. 

 

The outer two plates now have to move together on the main bolt even though they will have some wiggle room between them. Back off these two plates from the first one just enough to align the ends of the thumb screws with the dimples in the first plate. Thread the thumb screws in some more till they bottom into the dimples of the first plate. Next the SET screws in the last outer plate are tightened into the middle plate. As the set screws are tightened they might tend to 'walk' the outer plate around in relation to the middle plate. You want to make sure the thumb screws stay centered in the smooth holes of the outer plate - NO binding of the thumb screws on the sides of the smooth holes in the outer plate. 

 

You are done. The thumb screws and first two plates are a normal clutch. The third outer plate is like a lock nut that holds the system to the center bolt and keeps the clutch from rotating on the bolt. Strictly visualizing isn't easy.  Apply the above directions to an actual set and it will become quickly obvious. 

 

The RA setting circle (hour circle) does not touch any of the 3 plates. The setting circle is mounted to the black collar bolted to the brass gear. 


Edited by apfever, 25 February 2021 - 07:31 PM.



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